The present invention relates to positioning drives of the type comprising an output shaft whose speed can be increased by activating an electromagnetically activated clutch which couples the shaft to the drive shaft of an electric motor, and whose speed can be decreased by activating an electromagnetically activated brake, and provided with a negative-feedback speed regulating system, as well as with a positioning system operable for causing the output shaft to stop in a commanded angular position.
Two principal requirements are placed upon positioning drives of the type in question. One is that the output shaft, when commanded to stop at a predetermined angular position, do so very quickly, i.e., the decrease of speed from current operating speed down to zero speed should be effected within the shortest possible time. The other is that when the output shaft is thusly stopped, it be stopped very exactly at the angular position desired. The realization of these two requirements is often very difficult to effect in practice, especially when the driven load fluctuates. Such problems arise, for example, when such positioning drives are used to drive sewing machines, winding machines, machine tools, and the like.